The present invention relates generally to arrangements in paper machine press sections for equalizing the compression pressure in a press nip.
More particularly, the invention relates to a method in a paper machine press section by which compression pressure in a press nip is equalized, in which method the paper web is passed through at least one press nip formed by two opposed press rolls and through which at least one water-receiving press fabric is passed for receiving water pressed from the web in the press nip.
The invention further relates to a paper machine press section comprising at least one press nip formed between two opposed press rolls and wherein at least one water-receiving press fabric passes through the nip.
The invention additionally relates to a resilient loop component, which may comprise a resilient belt and/or a corresponding resilent coating of a press roll, which passes through a paper machine roll press or an extended-nip roll press and which is formed at least in part of elastic material.
Press sections of paper machines generally comprise one or more press nips through which the web runs in contact with or between one or a pair of press felts. The press felts generally comprise a woven framework layer onto the side surfaces of which nap layers of fibrous material are applied by pinning. Such conventional press felts have several drawbacks such, for example, as limited wear resistance. Moreover, the properties of the press felts tend to change during operation as the felts wear.
A substantial drawback of conventional press felts is that they tend to apply compression pressure to the fiber network of the web in an uneven fashion so that even under best circumstances the pressure is applied to the web only over about 30% of the area that is being compressed. The uneven distribution of the compression pressure results largely from the coarseness of the surface of the nap layer of the press felt, from the differences in compression applied by the felt caused by the yarns in the framework layer of the press felt, and from variations in the thickness of the press felt over a wider area thereof. The differences in compression pressure also are the result of the roughness of the surface of the press roll, for example a rock roll, by deviations in the shape of the surface of the press roll and by the bores or grooves present in hollow-surface press rolls.
It can be shown experimentally that if a uniform surface pressure is applied to the paper web being compressed, for example by using porous, smooth sinter sheets rather than conventional press felts, the dry solid content of the web is improved from about 45%, obtained by conventional press felts, to about 70%.